On a typical internal combustion engine vehicle, a significant amount of energy is wasted as the engine generates creep torque when the brakes are applied in the 0 to 6 mph range, and a significant amount of kinetic energy is lost in higher vehicle speed ranges when the brake is applied but the engine continues to burn fuel. However, on an electric vehicle, where energy conservation is extremely important to maximize vehicle driving range, it is highly desirable to provide a method of controlling electric motor torque in the vehicle to improve vehicle performance and energy conservation, particularly in the creep torque range and high speed braking range.
For purposes of this disclosure, it is important to understand electric vehicle related terminology. "Brake regen" is a term referring to the creation of regenerative torque, as a function of the brake signal input, which opposes the direction of vehicle travel, causing the motor to produce a regenerative current into the electric vehicle battery. The torque produced aids the mechanical brakes in reducing the vehicle speed. In other words, when the brakes are applied at a high vehicle speed, the negative torque generates a current to the battery which recharges the battery and assists in slowing the vehicle by slowing the motor.
"Compression regen" is a term which refers to the creation of regenerative torque, as a function of vehicle speed and accelerator pedal position, which opposes the direction of vehicle travel, causing the motor to produce a regenerative current into the electric vehicle battery. The amount of torque produced is set to emulate the engine compression drag feel of an internal combustion engine vehicle.
"Creep torque" is a term which refers to the creation of motor torque under zero accelerator depression which causes the vehicle to move forward when the vehicle is at lower speeds, typically between 0 to 6 mph. The amount of torque produced is set to emulate the creep forward driving feel of an internal combustion engine vehicle.
Accordingly, it is desirable to provide a method of controlling electric motor torque in an electric vehicle in which both regenerative (negative) torque is produced at higher speeds during braking and "creep" (forward) torque cancellation is provided at lower speeds.